PESTS OF COTTON

North Carolina Cooperative Extension
Extracted from INSECT and related PESTS of FIELD CROPS (AG-271)
Dated 5/82
Placed on the Web 10/94 by the Center for Integrated Pest Management, NCSU

In 1980, cotton was planted on 25,506 hectares (63,000 acres) of North Carolina
farm land. Cleveland County, the Scotland-Robeson counties area, and the
Northampton-Halifax-Edgecombe counties area produce 90 percent of the cotton in
North Carolina. Insects are an important factor in cotton production here but
only the bollworm and the boll weevil are considered limiting. A pest management
approach of varying degrees of sophistication has been applied for insect control
in all cotton-producing areas of our state.

Key to Pests of Cotton

A. Insect and mite pests which pierce or rasp plant tissue to extract sap
(Fig. A to D).

Aphids

- Usually feeding in colonies, these yellow, green or black,
pear-shaped insects (Fig. A above) may be as long as 2 mm and may or may not have
wings. Infested leaves curl and pucker; heavily infested seedlings become stunted
and die. A black mold, which grows on the sticky, sugary "honeydew" that aphids
excrete, is often evidence of aphid infestation.

-
Approximately 6.4 mm long, this oval-shaped, brown
lygus bug (Fig. B above) has long legs, long antennae, and a white triangle between
its "shoulders." It extracts sap from terminals, squares, flowers, and bolls,
causing young fruiting forms to be shed. Infested flowers and bolls may open
prematurely.

- The almost microscopic, eight-legged, adult
female mite is yellowish (Fig. D above) to dark green with 2 or 4 dark spots on its
back. The immature mite may have 6 or 8 legs. Feeding on the underside of the
leaf, this mite extracts sap, causing the upper leaf surface to have a whitish
or bronze cast. Severe infestations can result in defoliation and loss of plant
vigor. Silken webs are common on the underside of infested leaves, particularly
along the large leaf veins.

B. Caterpillars that chew or mine the foliage or sever seedling stems.

Armyworms

- These smooth-skinned, variously colored caterpillars
have 5 pairs of prolegs, are occasionally problem foliage pests, and may
be difficult to control chemically.

- This
dark-headed (Fig. A above), green or black larva
sometimes has 3 longitudinal, light stripes and usually attains a length of 25
to 30 mm. A small black spot occurs on each side of the second segment behind the
head (Fig. B above). This larva normally skeletonizes foliage but at times feeds on
squares, blooms, and bolls causing economic loss to cotton.

Fall armyworm - Although this green, brown, or black caterpillar
primarily attacks blooms, squares, and bolls, it also feeds on the foliage,
occasionally tops plants, and bores into stems. This larva has 5 pairs of
prolegs, reaches a maximum length of 40 mm, and often has distinct inverted "Y"
on its head capsule (Fig. C above). It has a black, longitudinal stripe down each
side of its body and a yellowish-gray stripe down its back.

Yellowstriped armyworm
- Reaching a length of up to 45 mm, the smooth-skinned, pale gray to jet
black caterpillar has a yellowish-orange stripe along
each side and a pair of black, triangular spots on the back of most segments
(Fig. D above). Like the fall armyworm, this larva often has a pale but distinct
inverted "Y" on its head capsule (Fig. E above). This insect rarely reaches
damaging levels on cotton but is most injurious to seedlings.

- Reaching a length of about 40 mm, this green
caterpillar has 3 pairs of prolegs and several longitudinal, white
stripes. Its body tapers from rear to front. Its feeding leaves ragged holes in
the foliage.

Cutworms.

These fat caterpillars reach a length of 40 or 45 mm and have
5 pairs of prolegs. They display a variety of feeding habits and curl
up when disturbed. They sever seedling stems and occasionally feed on leaves.

-
The skin of this light gray to black cutworm is
granulated, the granules resembling rounded, flattened pebbles (Fig. A). The
caterpillar cuts seedlings off at the soil line during the night. It commonly
pulls the cut stem of a seedling into the entrance of its burrow and feeds on it
during the day.

- This cutworm has a pale brown head, a dark brown
band down its back and brown sides with faint stripes. The skin granules of this
cutworm are like blunt cones as high as they are wide (Fig. B). The
caterpillar also severs seedlings near the soil line at night.

- Although primarily damaging to seedling stems, this
species is a climbing cutworm and may feed on foliage. Its smooth-skinned body
is pale gray to dark brown with a row of orange or yellow spots down the middle
of its back. A black spot and a yellow spot occur on the eighth abdominal
segment.

- About 8.5 mm long, the reddish-brown or gray adult
weevil (Fig. B) has a distinctive characteristic: a double-toothed spur on the
inner surface of each front leg. The female punctures squares and young bolls to
lay eggs. These nipple-like egg punctures are about 1 mm in diameter.
Egg-punctured squares flare and fall to the ground where larval development is
completed.

Caterpillars

- These moth larvae have 3 pairs of short legs near the
head and 5 pairs of prolegs.

- When
fully grown, these larvae are green, reddish,
or brown with pale, longitudinal stripes and scattered, black spots. Early
instars are cream colored or yellowish-green with few markings. Larval instars
vary from 1.5 to 44 mm in length and have 5 pairs of prolegs. The contents of
squares or bolls may be completely consumed by bollworms. Cotton lint development
is reduced and rot organisms may gain entrance into the bolls that are only
partially damaged.